Interface systems for use in transferring heat produced from a heat-dissipating electronic component to a heat dissipator or heat sink are well-known in the art. In this regard, such electronic components, the most common being computer chip microprocessors, generate sufficient heat to adversely affect their operation unless adequate heat dissipation is provided. To achieve this end, such interface systems are specifically designed to aid in the transfer of heat by forming a heat-conductive pathway from the component to its mounting surface, across the interface, and to the heat sink.
In addition to facilitating the transfer of heat, certain applications further require electrical insulation. Accordingly, such interface systems are frequently further provided with materials that are not only effective in conducting heat, but additionally offer high electrical insulating capability. Among the materials frequently utilized to provide such electrical insulation are polyimide substrates, and in particular KAPTON (a registered trademark of DuPont) type MT.
Exemplary of such contemporary thermal interfaces are THERMSTRATE and ISOSTRATE (both trademarks of Power Devices, Inc. of Laguna Hills, Calif.). The THERMSTRATE interface comprises thermally conductive, die-cut pads which are placed intermediate the electronic component and the heat sink so as to enhance heat conduction therebetween. The THERMSTRATE heat pads comprise a durable-type 1100 or 1145 aluminum alloy substrate having a thickness of approximately 0.002 inch (although other aluminum and/or copper foil thickness may be utilized) that is coated on both sides thereof with a proprietary thermal compound, the latter comprising a paraffin base containing additives which enhance thermal conductivity, as well as control its responsiveness to heat and pressure. Such compound advantageously undergoes a selective phase-change insofar the compound is dry at room temperature, yet liquifies below the operating temperature of the great majority of electronic components, which is typically around 51Exc2x0 C. or higher, so as to assure desired heat conduction. When the electronic component is no longer in use (i.e., is no longer dissipating heat), such thermal conductive compound resolidifies once the same cools to below 51Exc2x0 C.
The ISOSTRATE thermal interface is likewise a die-cut mounting pad that utilizes a heat conducting polyimide substrate, namely, KAPTON (a registered trademark of DuPont) type MT, that further incorporates the use of a proprietary paraffin based thermal compound utilizing additives to enhance thermal conductivity and to control its response to heat and pressure. Advantageously, by utilizing a polyimide substrate, such interface is further provided with high dielectric capability.
Additionally exemplary of prior-art thermal interfaces include those disclosed in U.S. Pat. No. 5,912,805, issued on Jun. 15, 1999 to Freuler et al. and entitled THERMAL INTERFACE WITH ADHESIVE. Such patent discloses a thermal interface positionable between an electronic component and heat sink comprised of first and second generally planar substrates that are compressively bonded to one another and have a thermally-conductive material formed on the outwardly-facing opposed sides thereof. Such interface has the advantage of being adhesively bonded into position between an electronic component and heat sink such that the adhesive formed upon the thermal interface extends beyond the juncture where the interfaces interpose between the heat sink and the electronic component.
The process for forming thermal interfaces according to contemporary methodology is described in more detail in U.S. Pat. No. 4,299,715, issued on Nov. 10, 1981 to Whitfield et al. and entitled METHODS AND MATERIALS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE; U.S. Pat. No. 4,466,483, issued on Aug. 21, 1984 to Whitfield et al. and entitled METHODS AND MEANS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE; and U.S. Pat. No. 4,473,113, issued on Sep. 25, 1984 to Whitfield et al. and entitled METHODS AND MATERIALS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE, the contents of all three of which are expressly incorporated herein by reference.
In addition to the construction of thermal interfaces, there have further been advancements in the art with respect to the thermal compositions utilized for facilitating the transfer of heat across an interface. Exemplary of such compounds include those disclosed in U.S. Pat. No. 6,054,198, issued on Apr. 25, 2000 to Bunyan et al. and entitled CONFORMAL THERMAL INTERFACE MATERIAL FOR ELECTRONIC COMPONENTS, and U.S. Pat. No. 5,930,893, issued on Aug. 3, 1999 to Eaton and entitled THERMALLY CONDUCTIVE MATERIAL AND METHOD OF USING THE SAME, the teachings of which are expressly incorporated by reference.
In addition to being able to facilitate the transfer of heat and provide electrical insulation, many interface systems additionally employ a grounded substrate formed from a conductive material, such as copper, to suppress radiated emissions, namely electromagnetic interference (EMI), generated in high frequency transistor applications. In this regard, such grounded substrate is utilized to minimize capacitance to the heat sink to which it is attached, as well as to provide shielding effectiveness and attenuation of radiated EMI. With respect to the latter, it has been shown that electrically grounded copper substrates can provide shielding effectiveness to 60 dB at 1000 KHz, which is an attenuation percentage of 99.9%.
One such commercially-available thermal interface incorporating a grounded conductive substrate is EMI-STRATE (a registered trademark of Power Devices, Inc. of Laguna Hills, Calif.). Such interface comprises a grounded copper substrate sandwiched between two polyimide film substrates, the latter being comprised of KAPTON-type MT. The exterior sides of such interface are further coated with a proprietary thermal compound to thus facilitate the transfer of heat away from the electronic component to a heat sink.
Notwithstanding the effectiveness of thermal interfaces currently in use, a substantial need exists in the art for an interface that provides greater EMI attenuation, shielding effectiveness, and thermal conductivity. In this regard, newer electronic componentry continues to have ever increasing power dissipation and EMI emission. While such electronic componentry typically is constructed and/or packaged to be electrically isolated, the aforementioned increases in power dissipation and EMI emission currently present drawbacks that must be addressed if such componentry is to perform optimally. Additionally, as such advances are made in such componentry, it is certain that the aforementioned concerns regarding radiated emission and power dissipation will continue to create a demand for an interface system that can adequately address the same.
Prior art interface systems, however, are ill-suited to meet such needs insofar as such interface systems, because of their multiple-layer construction, substantially reduces the flow of heat thereacross. In this regard, it has been found that the use of thermal interface systems having six layer construction does not provide desirable heat transfer from a given electronic component to a heat sink. Moreover, not only does each individual layer impede heat flow, but, as those skilled in the art will appreciate, each interface of adjacent layers additionally inhibits heat flow. In this respect, each layer contributes three distinct impediments to heat flow, namely, each layer introduces the material of which the layer itself is comprised, as well as the two interfaces at either surface of the layer. Thus, it will be appreciated that it is highly desirable to minimize the number of layers, and consequently the number of interfaces, comprising such interface system. In addition to the foregoing, it should be noted from a practical standpoint that manufacturing such interface systems having multiple layers is expensive.
In addition to the need for improved interface systems is the need for improved heat sinks to be used therewith that are capable of more effectively and efficiently dissipating the heat transfer thereto. In this regard, most heat sinks in use, which are typically fabricated from extruded aluminum, are formed to have a base with a plurality of fins extending therefrom. The fins are equidistantly spaced from one another and are formed to have sufficient surface area to dissipate the heat into the surrounding air. In this respect, a fan is frequently used to assure adequate circulation of air over the fins, so as to maintain desirable heat dissipation therefrom.
Unfortunately, however, the number of fins and the spacing therebetween is limited by the aluminum extrusion process. As is well-known, fins spaced closer together than 0.2 inches tends to block natural convection air flow and cannot be optimized for use in forced convection. Additionally, conventional extrusion technology limits the amount of surface area, namely, the height of the fins of the heat sink, which further constrains heat removal. In this respect, it is well-known that the amount of surface area is proportional to the amount of heat that can be removed. Hence, a decrease in surface area thus translates into limited heat removal.
To partially address the aforementioned inadequacies with extruded aluminum heat sinks has been the introduction of folded-fin heat sinks. Such assemblies comprise a relatively thin base section and a set of fins folded into corrugated sections mounted thereon. The base section is typically formed to be either very thin to reduce mass or, alternatively, thicker to act as a heat spreader. The folded fins coupled to the base act as a heat-transfer area, allowing a stream of forced air to remove heat from the base. Currently, such folded-fin heat sinks offer the maximum potential in surface area and reduced weight. In this respect, thermal resistance as low as 0.40Exc2x0 C./W can be reached with folded-fin assemblies in forced-air cooling at 500 ft/min of air velocity. Moreover, in utilizing a corrugated piece of aluminum or copper, there is thus eliminated the restrictions otherwise faced in the extrusion process.
Notwithstanding the desirability of such folded-fin heat sinks, the same still suffer from the drawback of failing to achieve optimal heat transfer and dissipation insofar as current folded-fin heat sinks fail to achieve optimal heat transfer from the base to the folded-fin assembly coupled thereto. As such, the maximum amount of heat that could otherwise be dissipated by the assembly is not attained.
Accordingly, there is a need in the art for a thermal interface that provides greater thermal conductivity and greater electrical insulation than prior art interfaces. There is additionally a need in the art for such a thermal interface that is of low cost, easy to manufacture, and may be readily utilized with existing componentry requiring the integration of a thermal interface system. Moreover, there is a need in the art for an improved heat sink that is more effective and efficient at dissipating heat transferred thereto from an electronic component. There is further a need for such an improved heat sink that is particularly more effective in transferring heat from a given heat source to the fins or other apparatus by which the same is dissipated.
The present invention specifically addresses and alleviates the aforementioned deficiencies in the art. Specifically, the present invention is directed to an interface system for use with electronic componentry that has superior electrical insulation and thermal conductivity properties than prior art systems. In the preferred embodiment, the interface system of the present invention comprises the combination of a generally planar substrate, preferably being comprised of a non-conductive material having a high dielectric strength. The planar substrate defines two outwardly facing flatwise surfaces that are configured to mate with the interface surfaces formed on the electronic component and the interface surface formed on the heat dissipator or heat sink, on the other surface Each respective outwardly facing surface has formed thereon a layer of a thermally conductive compound having a high degree of thermal conductivity to thus further facilitate the transfer of heat. In a preferred embodiment, such compound is preferably formed to have selective phase-change properties whereby the composition exists in a solid phase at normal room temperature, but melts, and therefore assumes a liquid phase, when subjected to the elevated temperatures at which the electronic component usually operates.
The present invention further includes an improved heat sink that is more efficient and effective in dissipating heat transferred thereto via an electronic component. Specifically, such improved heat sink comprises the combination of a base plate attachable to a heat-dissipating component and a folded-fin assembly compressively attached thereto. In a preferred embodiment, the heat sink is provided with one or more pressure clips (or other fastener arrangement) detachably fastenable to the baseplate that apply a compressive force, via a pressure spreader engagable therewith, against the folded-fin assembly that causes the assembly to remain compressively bonded with the baseplate from which the heat to be dissipated is received. To further facilitate the transfer of heat from the baseplate to the folded-fin assembly, there is preferably provided upon the baseplate a layer of a thermally-conductive compound having selective phase-change properties (i.e., liquefies during the operational temperature of the electronic component coupled to the heat sink), to eliminate any air gaps or voids between the baseplate and folded-fin assembly that would otherwise impede the transfer of heat. Alternatively, to the extent a greater degree of electrical isolation is desired, a thermal interface having a high dielectric capability may be interposed between the baseplate and folded-fin assembly.
The present invention thus provides a thermal interface system that provides both electrical insulation and sufficient thermal conductivity to effectively facilitate the removal of heat therefrom more so than prior art interface systems.
The present invention further provides a thermal interface having electrical isolation capability that utilizes a minimal number of layers in the construction thereof.
Another object of the present invention is to provide a thermal interface that is relatively simple and inexpensive to manufacture compared to prior art interface systems, and may be readily and easily utilized in a wide variety of commercial applications.
Another object of the present invention is to provide an improved heat sink that is more effective and efficient at dissipating heat transferred thereto from an electronic component, and especially more so than conventional heat sinks formed from extruded aluminum.
Another object of the present invention is to provide an improved heat sink that is capable of more effectively transferring heat received thereby to the heat-dissipating component thereof than prior art heat sinks.
A still further object of the present invention is to provide an improved heat sink that is of simple construction, may be readily and easily fabricated from existing materials well-known to those skilled in the art, is relatively inexpensive, and may be readily and easily utilized in numerous commercial applications.